Rapamycin is a macrolide antibiotic produced by Streptomyces hygroscopicus. It binds to a FK506-binding protein, FKBP12, with high affinity to form a rapamycin:FKBP complex. Reported Kd values for that interaction are as low as 200 pM. The rapamycin:FKBP complex binds with high affinity to the large cellular protein, FRAP, to form a tripartite, [FKBP:rapamycin]:[FRAP], complex. In that complex rapamycin can be viewed as a dimerizer or adapter to join FKBP to FRAP. Formation of the complex is associated with rapamycin's various biological activities.
Rapamycin is a potent immunosuppressive agent and is used clinically to prevent rejection of transplanted organs. Rapamycin and/or its analogs, CCI 779 (Wyeth) and SDZ Rad (“RAD001”, Novartis) are promising agents for treating certain cancers, for immune suppression and/or for helping to decrease the incidence of restenosis following interventional cardiology. Rapamycin has also been shown to have activity as an antifungal agent, in the experimental allergic encephalomyelitis model (a model for multiple sclerosis), in the adjuvant arthritis model (for rheumatoid arthritis), in inhibiting the formation of IgE-like antibodies, and for treating or preventing lupus erythematosus, pulmonary inflammation, insulin dependent diabetes mellitus, adult T-cell leukemia/lymphoma, and smooth muscle cell proliferation and intimal thickening following vascular injury. See e.g. US Pat. appln 2001/0010920.
Because it serves as an adapter to complex FKBP with FRAP, rapamycin is also capable of multimerizing appropriately designed chimeric proteins incorporating domains derived from FKBP and FRAP, respectively. Because of that activity, rapamycin and various derivatives or analogs thereof have also been used as multimerizing agents for activating biological switches based on such chimeric proteins. See e.g., WO96/41865; WO 99/36553; WO 01/14387; Rivera et al, Proc Natl Acad Sci USA 96, 8657-8662; and Ye, X. et al (1999) Science 283, 88-91.
Rapamycin's potential for providing relief from such an important swath of cruel diseases has stimulated the search for rapamycin analogs with improved therapeutic index, pharmacokinetics, formulatability, ease or economy of production, etc. The resulting investigation by the pharmaceutical industry and academic researchers has been a sustained one over the past few decades. This has led to the exploration of materials and methods for effecting chemical transformations of rapamycin, including reductions of ketones, demethylations, epimerizations, various acylations and alkylations of hydroxyls, etc.
A large number of structural variants of rapamycin have now been reported, typically arising as alternative fermentation products and/or from synthetic efforts. For example, the extensive literature on analogs, homologs, derivatives and other compounds related structurally to rapamycin (“rapalogs”) include, among others, variants of rapamycin having one or more of the following modifications relative to rapamycin: demethylation, elimination or replacement of the methoxy at C7, C42 and/or C29; elimination, derivatization or replacement of the hydroxy at C13, C43 and/or C28; reduction, elimination or derivatization of the ketone at C14, C24 and/or C30; replacement of the 6-membered pipecolate ring with a 5-membered prolyl ring; and alternative substitution on the cyclohexyl ring or replacement of the cyclohexyl ring with a substituted cyclopentyl ring. Additional historical information is presented in the background sections of U.S. Pat. Nos. 5,525,610; 5,310,903 and 5,362,718. See also U.S. Pat. No. 5,527,907. Materials and methods have even been developed for the remarkably effective and selective epimerization of the C-28 hydroxyl group (WO 01/14387).
New rapalogs with reduced immunosuppressive activity and/or interesting pharmacokinetic or bioavailability profiles would be very desirable for use as multimerizing agents or antifungal agents.
New rapalogs with attractive physicochemical or functional characteristics, e.g., in therapeutic index, bioavailability, pharmacokinetics, stability, etc., would also be of interest for a variety of pharmaceutical uses such as are mentioned above, including among others use as immunosuppressants, as anticancer agents and in reducing the incidence of restenosis following interventional cardiology (e.g. on drug-bearing stents).
The only rapalogs thought to be in clinical development as immunosuppressants at present are those with rather modest, conventional structural modifications, i.e., acylation or alkylation at C-43 (CCI-779 and SDZ RAD, respectively; see e.g., Yu, K. et al., Endocrine-Related Cancer (2001) 8, 249-258; Geoerger, B. et al., Cancer Res. (2001) 61 1527-1532) and Dancey, Hematol Oncol Clin N Am 16 (2002):1101-1114. Stents bearing a tetrazole-substituted rapalog, ABT-578, but having only a shortened biological half-life (see e.g. WO 03/022807 and 99/15530) are reportedly being studied too.
The invention described below represents a rather dramatic departure in the design of new rapalogs based on the incorporation of a phosphorus-containing moiety.